Resistance sine wave generator



Dec. 28, 1948. A. G. RICHARDSON ETAL 2,457,178

RESISTANCE SINE WAVE GENERATOR Filed Dec. 6, 1943 2 Sheets-Sheet 1 INVENTORS AVE/P) 6. lP/CHA/PDSON TREVOR H. CLAW/f BY X .A TTORNEY Dec. 28, 1948. A. cs. RICHARDSON ETAL RESISTANCE SINE WAVE GENERATOR Filed Dec. 6, 1943 I, '8 my? a 2 Sheets-Sheet 2 ATTORNEY Patented Dec. 28, 1948 UNITED STATES PATENT OFFICE RESISTANCE SINE WAVE GENERATOR Avery G. Richardson, Boonton, N. 1., and Trevor H. Clark, New York, N. Y., alaignora to Federal Telephone and Radio Corporation, New York,

N. Y., a corporation of Delaware I Application December 6, 1948, Serial No. $13 ,198 1% Claims. (01. 115-404) 1 Our invention relates to converters, and more particularly to a device for transforming a direct voltage into an alternating voltage.

For numerous purposes, for example for use be graded, or the individual resistors must be of various values to produce a sinusoidal output, this type of converter is difficult to accurately construct and the cost, has naturally been high.

It is an oblect'of our invention therefore to provide a simple and inexpensive device for converting a direct voltage into an alternating volt- It is a further object of our invention to provide means for converting a direct voltage into an alternating voltage, the frequency and instantaneous phase of which is a direct function of the angular position of a rotating shaft.

According to a feature of our invention, we provide means for obtaining a pure sine wave output from a resistor by connecting the resistor to a source of direct current, positioning a pair of brushes in contact with the resistor, and producing a relative rotary movement between the resistor and the brushes.

According to a further feature of our inven-' tion, we provide for a variation in the amplitude of the voltage obtained from such a device by changing the spacing between the brushes.

An additional object of the invention is to provide such a device with a second pair of brushes for producing a second sine wave output, and to permit adjustment of the phase of the two wave outputs by altering the relative angular positionof the two pairs of brushes.

The invention may further provide means for reducing the wear resulting from the pressure of the brushes against the resistor by utilizing a series of parallel conducting members positioned on the surface of the resistor at right angles to the direction of current flow, so that such members act as commutating segments.

Other objects and advantages will be apparent form of the invention and from the drawings, in which:

Fig. 1 is a side elevational view or a preferred form of apparatus embodying the present invention;

Fig. 2 is a front elevational view of certain of the elements of Fig. 1;

Fig. 3 is a side elevational view of a modifl- A cation of Fig. 1, showing an alternative means for producing relative rotation between the resistor and brush members;

Fig. 4 is a plan view of a modified form of brush holder for use in the mechanism of Fig. 1;

Fig. 5 is a sectional view of Fig. 4 along the line 5-5;

Fig. 6 is a plan view showing a series of commutating segments applied to the surface of the resistor of Figs. 1 and 2;

Fig. 7 is a side elevational view of Fig 6; and Fig. 8 is a plan view of. a modified form of the resistor and conducting bar assembly of Figs. 1 V

and 2.

'In Fig. 1 is shown a'resistor housing 9 composed of insulating material and supportedon a base It. Housing 8 is formed'with a cut-out portion ii adapted to receive a block or sheet of homogeneous resistance material l2, as illustrated. This resistance material I2 may comprise, for example, carbon or carbon Bakelite, and may be of any degree of thickness necessary or desirable. If a sheet relatively thin is employed, a backing of insulating material may be added for support and to prevent distortion. Two bars or strips i4 composed of conducting material such as copper overlie the upper and lower ends of the block. Resistor l2 and its two end bars I4 preferably but not'necessarily constitute a unitary assembly, this assembly being inserted into the cut-out portion ll of housing 8 and held in place by suitable means such as a screw It.

Two binding posts It on the rear surface of housing I are connected to a suitable. source of direct current such as battery 20. These binding posts in turn are respectively connected in any conventional manner to conducting bars ll as indicated in Fig. 1. By means of this construction direct current from source 20 will be fed t0 the upper and lower ends. of resistor block I2,

and due to the homogeneous nature of the resistance material and the spreading effect of conducting bars I, the current flow through the resistor will be substantially evenly distributed. Thus, equi-potential lines will .be created which will be straight and parallel to the bars I.

from the following description of a preferred Also shown in Fig. 1 is a motor or other source shaped spring caps 28 in a conventional manner.

Shaft 24 is perpendicular to the surface of the resistor, so that upon rotation of the shaft brushes 28 will describe a circular path on its surface.

Fig. 2, which is a front elevational view of a portion of Fig. 1, shows two oppositely-disposed U-shaped openings 34 formed in brush holder 28. these openings 84 respectively receiving the brushes 28, with their caps 28. Due to the shape of the openings, the brushes may be adjusted in a radial direction so as to change their radial spacing both with respect to each other and to the shaft 24. A pair of screws 38 are respectively associated with the U-shaped openings 84, so that the sides of the openings may be pinched together to hold the brush caps 29 in any selected position. Furthermore, due to the square shape of the caps 28, the brushes 28 are prevented from turning or twisting within openings 34.

Caps 28 are electrically connected respectively to a pair of slip rings 82, by means such as leads ll, these leads being partially molded within holder 24. A second pair of brushes 88 are associated with slip rings 82, and these latter brushes are in turn connected to a load as indicated in Fig. i.

It is believed that the operation of the device of Figs. 1 and 2 will now be clear. It has been stated that the current flow through resistor I2 is substantially uniform, creating equi-potential lines which, in the drawing. will be horizontal. .When brushes 28 are rotated about the axis of shaft 24 by motor 22, they will out these equi-potential lines at varying rates depending upon the speed of rotation of the shaft and the instantaneous position of the brush holder. With proper adjustment oi the brushes the voltage output delivered to the load will be substantially in the form of a sine wave. having its maximum when the brush holder is in the postion shown (vertical) and its minimum when the holder is in horizontal position. Adjustment of the brushes 28 radially by loosening of screws 38 will change the potential drop across the brushes and correspondingly the amplitude of the wave output.

In Fig. l the relative movement between the resistor block and its contacting brushes is produced by rotating the brushes. However, it may be desirable to instead rotate the resistor while the brushes remain stationary. In such circumstances the structure of Fig. 3 may be employed. In this figure is shown a stationary support 28 on base It positioning the two brushes 28 in insulatingly spaced-apart relation. The brushes 28 are connected respectively to two binding posts 48 in turn connected to a load.

Shaft 24 of motor 22 now rotates a housing 42 rigidly secured to the shaft. Housing 42 is formed of any suitable insulating material. A cut-out portion is provided in housing 42 to receive resistor l2 with its conducting end bars i4 in the same manner that the resistor assembly is received in the cut-out portion ll of housing 8 in the device of Fig. 1. Screw l8 performs the similar function in both figures of positioning the resistor block within the cut-out portion.

A pair of slip rings 48 formedintegral with housing 42 are respectively connected to conducing bars l4 in. any suitable manner. A pair of brushes 44 connected to source of direct current 28 contact slip rings 48 as illustrated. The electrical output of the structure of Fig. 3 is similar in all respects to that of Fig. 1. If desired, means may be provided for changing the radial position of brushes 28 in support 38 so that the amplitude of the wave output may be altered in a mannersimilar to that resulting from an ad- Justment of the screws 88 of Fig. 2.

Figs. 4 and 5 show a modified form of brush holder for producing a polyphase voltage output. Two pairs of square-shaped brushes 28a and 281) are provided respectively with spring caps 28a and 28b. Brushes 28a and caps 28a are mounted on a support 48 rigidly secured to shaft 24 as shown in Fig. 5. Brushes 28b and caps 29b are mounted on a ring-shaped support 48 partially encirclin a flanged portion of support 48. Support 48 has two arcuate recessed portions 49.

Whereas support 48 is rigidly secured to shaft 24, support 48 is not secured to the shaft and has a limited amount of angular movement relative to support 48 within the boundaries of recessed portion 48 as shown in Fig. 4. The relative position of members 48 and 48 may be maintained by means of a-screw 84 receivable in an opening in support 48.

Each of the brush supports 46 and 48 is equipped with a pair of slip rings 50 and 82 respectively to which the brush caps 29a and 28b are connected in any suitable manner, the caps 28a being illustrated as connected to slip rings by a pair of leads 3la which are partially molded within support 48. Further brushes connected to a load are associated with slip rings 58, 82 as shown in Fig. 5. By altering the angle between brushes 28a and 28b the phase relation of the voltage outputs can be varied. If the two sets of brushes are positioned apart then the second voltage will obviously be 90 out of phase with the first voltage.

Means may obviously be provided in the structure of Figs. 4 and 5 for changing the spacing between the brushes of each pair. This adjustment may be obtained, if desired, by an arrangement similar to that shown in Fig. 2.

The structure of Figs. 4 and 5, while intended for use with the apparatus of Figs. 1 and 2, may be modified to permit its use in conjunction with the mechanism shown in Fig. 3. That is, the four brushes may be stationary while the resistor rotates. Such a modification would involve only the proper positioning of a second set of brushes in support 38. One advantage to be derived from such an arrangement is that only two slip rings need be employed instead of four required by the structure of Fig. 5.

If it becomes necessary to minimize the wear on the resistor surface resulting tom the pressure of the brush members, an arrangement such as that shown in Figs. 6 and 7 may be employed. In these figures, the surface of the resistance material is covered with a film or layer of conducting material such as copper. This conductive film, such as 88 in Figures 6 and 7, is relatively thin in comparison with the resistor I2. A series of closely-spaced parallel slits are then cut in this conducting film at right angles to the direction of current fiow through the resistor. Thus the resulting strips of conducting material act as commutator segments in contact with the brush members. Since adjacent strips are not in contact with. one another, the uniform distribution of current along the surface of resistor I2 is maintained, and the voltage output from the device will not be affected.

ess and then engraved with a series of closely spaced parallel lines. It is also within the scope of the invention to provide other commutating devices, such for example as a wire wound spirally around the resistor l2 and then cut at every turn, or else a number of parallel spaced-apart conductive barsor strips maintained in any known manner on the surface of the resistor. Clearly other devices may also be employed which serve as equi-potential conducting elements in contact with the brush members, any of which may be substituted for the specific means illustrated or mentioned herein.

It is realized that sinusoidal output voltage is possible only with high impedance loads. when current is drawn by the load, it is possible to secure empirical correction by shaping the conductor bars ll at the ends of resistor 12 as shown in Fig. 8. With the ends of the conducting bars ll bent inwardly, and the adjacent surfaces of the resistance material made in convex-form to correspond therewith, then the vertical potential energy from a direct current source to said load,

drops along the resistor will vary from maximum at the center to minimum at the two sides. By proper shaping of the bars M with respect to any given load, a pure sine wave output can beobtained. 1

While we have described above the principles of our invention in connection with specific apparatus and particular modifications thereof, it is as to be clearly understood that this description is made only by way of example and not as a limitation on the scope of our invention as set forth in the objects of our invention and the accompanying claims.

We claim:

1. In combination with a load consuming a substantial amount of current, a converter for supplying true sine wave alternating current which comprises a flat resistance unit and output brushes movably engaging the face of said unit over a cyclic path, said unit consisting of a block of resistance material of uniform thickness and composition terminating at each of two opposite edges in a strip of highly conductive material, the junction line between the resistance block and each conductive strip and said}. cyclic path being so relatively shaped as to provide a true sine wave output potential at said brusheswhen direct current is supplied to the conductive strips and alternating current flows to the load.

I 2. A converter according to claim 1, wherein the path of said brushes is circular and said conductive strips and resistance block are shaped to present a junction line between said strips and block which enables correction for potential drops from said conductive strips to said movably engaging brushes due to flow of load current, thereby effecting a substanial sine'wave output when said load draws current.

3. A converter according to claim 1, wherein the conductive strips are shaped so that said junction lines are curved with concavity toward said brushes.

AVERY G.-R.ICHARDSON. TREVOR H. CLARK.

I aamanncrzs crrnp The following references are of record in the illc of this patent:

UNITED s'ra'rns Para-ms 

